1. Field of the Invention
The present invention relates generally to the field of improving the heat transfer resistance of a roof system in which insulation material is confined between construction members, and more particularly but not by way of limitation, to an insulated roof system which provides improved insulation qualities to a pre-engineered building and the like.
2. Discussion of Prior Art
The pre-engineered building industry has developed into a very large segment of the building construction industry in the United States, and it has experienced an increasingly greater share of the construction industry budget throughout the world. The established method of erecting the roof or wall of a pre-engineered building is to erect the building frame which is comprised of primary and secondary structural members supported by a foundation. Once the foundation is constructed, the primary structural members are erected and attached to the foundation; next, the secondary structural members are connected across the primary structural members. Appropriate bracing members are interconnected, and roll blanket insulation is placed either across or parallel with the secondary structural members and temporarily secured in place by weights or some other securing means.
The panel members are then disposed over the blanket insulation, and the panel members and underlying secondary structural members are connected together by fasteners. Typically, the attachment of roof panel members is done by workmen who stand on top of the panel members and attach the panel members to the underlying secondary structural members (which will usually be purlins or bar joists). The panel rests substantially on the underlying secondary structural member. The blanket insulation is compressed throughout the vicinity of the intersection of the panel and underlying secondary structural member. Compressed insulation has only a small fraction of its uncompressed insulating capacity. Blanket insulation placed perpendicular to the secondary structural, which is the usual case, and compressed between two objects such as the panel and the secondary structural member typically requires a distance of about five times its original thickness to recover to its full thickness. Thus a six inch blanket would require about 2.5 feet on both sides of the secondary structural to recover its full thickness. This resulting zone of compression substantially reduces the insulation's resistance to heat transfer.
The installation of insulation in the above described manner presents a major problem in the construction of pre-engineered buildings. As the panel members are connected to the underlying secondary structural members, the underlying blanket insulation, which is normally a compressible but nonelastic material, is compressed between the panel members and the secondary structural members. This compression of the insulation is undesirable, as it reduces or destroys the thermal effectiveness of the insulation.
The purpose of connecting the panel to the secondary structural member is to secure the panel members and to transfer externally imposed load from the panel members to the secondary structural members, which in turn transfers the stress to the primary structural members. These imposed loads create stress which may be tension, shear or compressive stress. As to the latter, compressive stress is created by inwardly directed live load which is transferred through the blanket insulation. As the panel members move relative to the secondary structural members during the life of the building, looseness occurs at the connector location, and it is difficult if not impossible to maintain watertightness at these connector points.
One prior art solution to this problem of compressed insulation is the provision of elastic insulation boards disposed between the insulation and the panel members. These insulation boards are located such that the panel rests on the insulation board which rests on the compressed blanket insulation, which is in turn supported by the underlying structural members. The insulation boards have an improved resistance to heat transfer, and in their immediate area create a better thermal barrier and spread the inwardly directed load that causes compression over a larger area of the glass fiber insulation. This decreases the amount that the insulation is reduced in thickness to some extent; however, the insulation is so weak structurally that no substantial improvement occurs. While this is an improvement over the previously described prior art method, it still has a number of shortcomings. Among these is the fact that the blanket insulation is still compressed between the insulation boards and the underlying structural members, and since the zone of compression in the blanket insulation extends well beyond the edge of the insulation board, there still exists a substantially reduced resistance to heat transfer. The insulation boards are expensive and difficult to install in that they must be held in place while the overlying panel is being connected. This is discussed in more detail in my earlier U.S. patent application entitled "Support Spacer Apparatus," Ser. No. 093,173, filed Nov. 13, 1979.
The need to transfer shear stresses from the panel to the underlying structural member is well-known in the pre-engineered building industry. This shear action requires that the force parallel to the plane of a panel be transferred through the fastening system to the underlying secondary structural members. While the use of insulation boards has helped somewhat in regard to increasing the thermal effectiveness of the roof to resist heat transfer, the shearing action on the panel to the underlying structural connector has become a greater problem. The reason for this is that the underlying structural is separated from the panel by a greater distance. This causes the offsetting shearing force to act through a greater moment arm and the connector must be correspondingly increased in strength or the force compensated for in some other manner. The problem of maintaining a watertight seal around the connector is more difficult with the use of such insulation boards.
Taylor, U.S. Pat. No. 3,394,516, taught the use of a spacer between the panel members and the secondary structural members to prevent the panel members from being pulled so close to the secondary structural members as to crush or compress the insulation. The Taylor spacer had a plurality of pointed stand-off legs that penetrated the insulation; the panel members were placed over the spacers, and sheet metal screws passed through the panel members to secure the panel members to the secondary structural members. The Taylor spacer is discussed in more detail in my above referenced U.S. patent entitled "Support Spacer Apparatus."
It is highly desirable to create a substantially uniform, effective resistance to energy transfer through building roofs and walls, and this can be accomplished by applying a uniform thickness of insulation material about the enclosed building surface, usually referred to as the "building envelope." A uniform resistance to heat transfer eliminates thermal short circuits, reducing air conditioning and heating costs. While the use of compressed blanket insulation has in the past had some inherent disadvantages, work with various other materials has generally been unsuccessful in providing an adequate substitute for blanket insulation. A building is basically a composite of numerous structural elements, and materials having good structural characteristics are normally poor thermal insulators, while good thermal insulators, on the other hand, normally are structurally weak.
Some designers have attempted to interweave materials having good structural characteristics with those which have good insulating characteristics to create a more effective building envelope. Among such various prior art insulation solutions of this type are structural surfacing materials such as steel or concrete with "spray on" materials such as isocyanurate or similar foams field-applied on the inside or outside of the structural surface material. Spray on materials have the potential advantage of covering the building surface, regardless of its configuration, in a relatively uniform manner. While this method eliminates thermal short circuits, the spray on materials also have numerous shortcomings. Among these are high costs resulting from the field labor involved; poor quality control which frequently leads to inadequate bonding so that the insulation often delaminates; and project delays because of inclement weather conditions.
Another prior art solution is represented by paneling systems which are factory- or field-assembled and are composed of various combinations of materials. Among the paneling systems that have been tried are laminated systems composed of one or more rigid facing materials with an appropriate semi-rigid insulation attached to the rigid material for support. Again, these systems are discussed more fully in my earlier mentioned U.S. patent entitled "Support Spacer Apparatus."
Some paneling systems, sometimes referred to as sandwich panels, have used relatively dense batt insulation of the glass fiber type and usually rely on perimeter framing to hold the insulation in place. The insulation either has to be strong enough to support its own weight without gradual crushing, or friction support must be employed. Friction from the insulation itself is often inadequate to hold the insulation in place and, as a result of vibration from wind or transportation, the insulation often becomes dislodged. The insulation itself is structurally weak and even support pins do not serve to prevent the insulation from settling when it is used as a vertically extending wall. In the past, this type of paneling system has been relatively expensive and has not solved the problem of preventing thermal short circuits through the insulation. Further discussion on this type of paneling system is provided in my above mentioned patents.
While many insulation methods have been attempted, the use of compressible blanket insulation remains to be the least expensive and most effective means of insulating a building structure, which accounts for its wide acceptance in the building industry. Of course, blanket insulation is totally effective only if the design of a building structure provides for maintaining uniform blanket insulation thickness and for keeping the insulation dry.
A typical blanket insulation consists of a light weight, highly compressible, structurally weak insulation material laminated to a light weight, relatively high tensile, impervious facing membrane that is laminated to the insulation. This laminated insulation layer and facing material is normally positioned and maintained in place while applying restraining force to the facing material through a friction connection. In normal practice, that friction connection compresses the insulation as discussed hereinabove, and this compression materially reduces or destroys the effectiveness of the insulation, creating numerous thermal short circuits in the wall or roof structure.
Alderman, U.S. Pat. No. 4,147,003, taught the use of straps to support a support trough for the placement of insulation between secondary structural members. This support trough serves only to insulate between the secondary structural members, while insulation at the secondary structural members is still achieved by semi-rigid insulation boards that are placed above the secondary structural members. Roof fasteners may pass through these insulation boards, and the above described problems are presented, resulting in serious thermal inefficiencies over the secondary structural members.
Laminated blanket insulation has been installed by clamping it between exterior panels and the underlying structural members as discussed above. This served the dual purpose of transferring load from the panel through the insulation to the underlying structural system while securing the insulation in place. Not only does the clamping of insulation between panel and structural members result in serious thermal inefficiencies, it also results in nonuniform tensile stress being created in the laminated material, leading to wrinkles across the facing of the blanket insulation. Thus, when the laminated material is visible in the interior of the building, a generally poor appearance results. The reason for this nonuniform tensile stress is that the beam strength of the panel between the fasteners that secure the laminated material is insufficient to exert adequate frictional force to spread the tensile load in the insulation facing uniformly across the width of the insulation.
In most instances, laminated insulation is simply cut below the bottom of the wall panel or at the edge of the roof panel, and the end of the insulation is exposed to rain, snow or other moisture. As a result, the insulation "wicks" water into the body of the insulation for a considerable distance along its length. This water further decreases the thermal efficiency of the insulation, and it also results in corrosion of the panel members, the base angles and other supporting parts. Another source for intrusive moisture is the breakdown of the vapor barrier caused by the uneven tensile stress exerted on the blanket insulation, resulting in stress tears and punctures.